1. Field of the Invention
The present invention relates to a back draft alarm assembly for combustion heating devices and, more particularly, to a back draft alarm assembly requiring a specific duration for a back draft occurrence before emitting an alarm and, most particularly, to a back draft alarm assembly employing a plurality of temperature sensors proximate a flue gas opening of the heating device.
2. Background Information
Combustion heating devices are widely used in residential and commercial buildings for heating fluids for use by residents. The devices include water heaters and furnaces providing hot water and internal heating for the building residents. Natural gas and liquid propane (LP) are commonly used for fuel in both furnaces and water heaters, although oil, coal and biomass (wood) find use in furnaces. These combustion heating devices are nearly always located within the building, often in a lower or basement level. The combustion gases formed during burning of the fuel must be vented to the exterior of the building structure. The heating device is connected to a chimney or vent stack that extends to the structure exterior for this purpose. Although some furnaces include piping to draw air from exterior the structure for combustion, many furnaces and nearly all water heaters employ an atmospherically vented system. The hot gases are of lower density and thus rise up the vent stack heating the stack interior. The venting system includes an opening in the chimney or vent stack, adjacent the furnace or water heater, that draws some air from interior the structure along with the combustion gases to move the gases up the chimney or vent stack.
For various reasons, these atmospherically vented stacks do not function properly to remove combustion gases formed in the heating device. For example, the vent stack may be partially or completely plugged by solids, or the building structure may be so tightly sealed that little internal air is available to carry the combustion gases up the vent stack. The result is termed “back drafting,” where combustion gases, including carbon monoxide, enter and remain within the building structure, causing a condition dangerous to the residents. Back drafting may be an intermittent problem for a combustion heating device and can be difficult to detect and monitor.
A number of patents concerned with the control and monitoring of various combustion heating devices have been granted.
Monette, in U.S. Pat. No. 4,751,912, describes a device for detecting the diversion of gas furnace or gas hot water heater exhaust into a dwelling due to chimney back drafting. The device detects a sustained rise in the temperature of the gases passing through the draft-diverter orifice. A significant rise in temperature indicates that the above condition has occurred. This temperature rise is recorded only after the condition has persisted for a sufficiently long period of time, thereby avoiding the recording of temporary back drafting conditions which are not required to be recorded. The device consists of a high temperature resistant plastic strip or other material with similar conductivity and specific heat qualities with a temperature sensitive color-change material mounted on the surface of the plastic strip at one end of the strip. This strip is attached to the furnace or gas hot water heater in a preferred location with the color-change material facing away from the normal flow of back drafting exhaust gases. Heat from the back drafting flow causes the color-change material to change color once the heat in the gas flow has penetrated through the underlying plastic strip. An aerodynamic stagnation zone on the front face of the plastic strip during a back draft condition prevents the color-change material from changing color prematurely.
In U.S. Pat. No. 4,856,982, Olson discloses an exhaust fan for exhausting combustion gases from a gas fired water heater, a gas pressure diaphragm switch for operating the exhaust fan in response to fuel flowing to the burner of the water heater, and a safety device for preventing fuel flow to the burner upon detecting undesirable changes in combustion gases. The apparatus further includes a time delay to continue operation of the exhaust fan and exhaust residual combustion gases for a short time after fuel flow to the burner has ceased. In one form, the time delay is a time delay relay switch and in another form it is a flow restricting orifice that restricts the flow of fuel from the gas pressure diaphragm switch, thereby maintaining a closed circuit to the exhaust fan.
Hall, in U.S. Pat. No. 5,158,446, describes a fuel-fired, forced draft heating appliance that includes a draft inducer fan having an inlet connected to a vent hood, an outlet connected to a vent pipe, and an interior housing region in which a negative pressure is generated during normal appliance operation. The vent hood receives hot combustion gases generated by the appliance, and has an inlet for receiving ambient dilution air that mixes with and cools the combustion gases entering the hood and subsequently is discharged into the vent pipe by the fan. A combination pressure and temperature limit control is used to sense the presence of an obstruction in either the vent pipe or the vent hood inlet and responsively shuts down the appliance. The control includes a vacuum switch external to the fan, a bimetallic disc-type temperature sensor disposed within the negative pressure fan region, and a conduit interconnecting the switch and the temperature sensor. During normal appliance operation, ambient air is drawn into the fan housing sequentially through the vacuum switch, the conduit and the temperature sensor. An obstruction in the vent pipe sufficient to reduce this air flow below a predetermined level causes the vacuum switch to responsively shut down the appliance. An undesirably high temperature within the fan, arising, for example, due to an obstruction in the vent hood inlet, causes the temperature sensor disc to block air flow through the conduit, thereby also causing the vacuum switch to responsively shut down the appliance.
In U.S. Pat. No. 5,261,389, Trieb discloses a power vent system for exhausting hot combustion gas by-products. The system includes a plenum or mixing chamber, a conduit system and an air aspirating discharge assembly. Negative pressure is developed in the plenum by a blower therein. Ambient air is drawn into the plenum from the atmosphere and mixed with the hot flue gases. The resulting cooled mixture is exhausted through the conduit system under pressure and, at the discharge assembly, additional ambient air is mixed with the mixture by a discharge assembly venturi effect, which also accelerates the gases away from the discharge assembly.
U.S. Pat. No. 5,280,802 by Comuzie, Jr., describes first and second sensors and alarm member mounted to a gas appliance. More particularly, the sensors are mounted to the diverter housing and adjacent a lower portion of the gas appliance for detection of spillage in the form of flue restriction relative to the first sensor. The second sensor provides roll-out sensing relative to gas fumes backed up in the flame portion of the gas appliance.
Cheek, in U.S. Pat. No. 5,531,214, describes a gas vent and burner monitoring system for monitoring a gas burner vent appliance. The system includes an alarm, a first sensor proximate the burner and a second sensor proximate the draft hood. Each sensor detects the occurrence of an event and the respective sensor activates the alarm when the event occurs. In a first embodiment, the sensors are temperature sensors. In an alternate embodiment, the temperature sensors are replaced with oxygen depletion sensors set to detect when the presence of oxygen is below a predetermined value. Further, the system may include a pressure sensor which trips the alarm when an increase in pressure in the pressurized chamber above normal operating levels is detected.
In U.S. Pat. No. 5,797,358, Brandt et al. disclose a multifunction controller for a water heater that includes a control panel and a plurality of sensors that monitor a variety of functions that impact the operation of a water heater. A flammable gas sensor, placed in proximity to the air intake, detects the presence of an unsafe concentration of gas and issues a signal to the control panel, which subsequently discontinues the operation of the burners. Detection of a blocked vent pipe is achieved by a carbon monoxide sensor placed near the draft hood. The control panel is equipped with circuitry which monitors usage of the heater for a specified time period to develop a pattern of use. Subsequent to the monitoring period, the controller will activate the burners a predetermined time prior to an anticipated period of high use. During periods of low use, the controller will decrease the temperature to which the water is to be heated, thereby resulting in a more efficient heater. Nonvolatile memory records data from the sensors are stored so that the operation status of the heater may be ascertained subsequent to a power outage. The control panel contains a plurality of visual alarms, each of which corresponds to a sensor. Consequently, repair and maintenance are simplified because the cause of a malfunction is quickly recognized.
Brown et al., in U.S. Pat. Nos. 6,044,835 and 6,102,030, describe a horizontal combined air intake and combustion gas vent terminal assembly having improved wind pressure response and anti-recirculation characteristics. The terminal has a vent conduit disposed inside an air intake conduit. A scoop assembly is provided at the intake conduit inlet to increase the intake air pressure at the inlet. The vent conduit is nozzle-like to throttle combustion gases, thereby accelerating the gases and permitting the terminal to project the gases away from the intake conduit terminal. The vent conduit is disposed asymmetrically with the intake conduit to further discourage mixing of intake air and combustion gases. The terminal may also be provided with a static pressure measuring means to provide an intrinsic safety shut down system within the terminal in case of a blockage of the intake or vent by snow, ice or other debris.
In U.S. Pat. No. 6,450,874, Hoyez et al. disclose a variable speed power flue ventilator with a thermostatically controlled motor cooling system. The thermostatically controlled cooling system employs an auxiliary motor cooling fan separate from the fan used by the power ventilator to extract exhaust gases. A thermostatic sensor switch actuates the motor cooling fan whenever the temperature in the exhaust fan motor housing rises to a preset value. The cooling fan then draws cool ambient air through the motor housing until the enclosed housing area reaches a second, lower, preset temperature at which point the cooling fan is shut off by the thermostat.
Thiessen et al., in U.S. Pat. No. 6,552,647, describe a monitor and control system that responds to alarm signals representing different hazardous conditions in an environment having a number of utility service supply lines, such as a home residence. One or more sensors coupled to the processor are each associated with one or more of the service supply lines. Each sensor produces an alarm signal in response to a hazardous condition attributable to an associated supply line. Each associated supply line is provided with a control device that is coupled to an output of the processor, and the processor is configured to produce one or more output signals in response to an alarm signal at a given input. Each control device is arranged to disable its associated supply line, with respect to a sensed hazardous condition, in response to a corresponding output signal from the processor.
In U.S. Pat. No. 6,715,451, Stretch et al. disclose a gas-fired water heater having a combustion chamber with a bottom wall defined by a perforated flame arrester plate forming a portion of a flow path through which combustion air may be supplied to a burner structure within the combustion chamber. During firing of the water heater, a combustion air shutoff system, having a heat-frangible temperature sensing structure disposed within the combustion chamber, senses an undesirable temperature increase in the combustion chamber. The temperature increase may be caused by a partial blockage of the flow path. The air shutoff system responsively terminates further air flow into the combustion chamber, thereby shutting down the burner, prior to the creation in the combustion chamber of a predetermined elevated concentration of carbon monoxide.
Weimer et al., in U.S. Pat. No. 6,726,111, describe a system and single controller for receiving constant and individualized information from a plurality of air control systems. A single controller is capable of controlling and interacting with at least two separate air control systems to control an environmental characteristic, and in the process, reduces the costs associated with the manufacturing and everyday operation of the individual systems. In addition, the controller is capable of intelligently communicating with the input and output devices of the system, and particularly with each individually interfaced appliance, such that the controller can adaptively control the system through the use of stored historical data.
Applicants have devised a back drafting alarm device that monitors and records each occurrence of a back draft condition for a combustion heating device over an extended period of time.